Module 7 - Tiffany

[hfboyce]

Module 7 Screen recordings

1. Working with other files - moving functions into your notebook

• Talk about how we recycle functions that we've written by saving them in a .py file so that we can use them again.
• Take the function exponent_a_list (In the comment here) and save it as a .py file in your folder.
• Next ask how do we bring these functions into our notebook? Copying and pasting is not adhering to the DRY principle, but we could import instead.
• Show them how to import exponent_a_list into the notebook.
• Next use the function in an example so they can see that it works.
• Ask for help by finding the docstring on the function with ?exponent_a_list .

2. Working with other files - pytest

• We wrote unit tests for the exponent_a_list function back in Module 6 (in the comment here). Explain that we can save these in a .py file like we did in our function exponent_a_list.
  • Note that this time we add each each assert into it's own function that calls no arguments. They might be wondering why we are doing this so tell them, it will be explain shortly.
  • Import our function exponent_a_list into the test .py file like we did in the previous section and save it as a new .py file.
• Show them now that they can import the test file into the notebook like before.
• Demonstrate that they can now call the test functions (remember that these don't have returns statements so nothing will be returned).
• We could now call each function individually or use pytest.
  • Pytest is a "Python testing tool that helps you write better programs" We can use it to test the functions we make.
• !pytest filname.py -This shows them that the tests (hopefully all pass). (explains why we separate our functions into separate tests)

If you want to show them a function that doesn't work for all the tests, you can show them this function and these tests located in this comment that will result in an error (hopefully).

3 Style Guides and Enforcement

• Ok so my idea for this is to first explain in a few regular slide what kinds of formatting should be used and what is good standards which you can record like a regular slide decks.

• Then after that, start a new recording where you implement flake8 and black. I think that will work better.

• Take a file with bad code (This code here from Tom's lecture 4 that i've pasted here)

• Show them the file and where it's saved.

• In a Jupyter notebook check for all the "grammar" mistakes using

  !flake8 filename.py

• Next show them the tool black and how it follows a slightly different styling guide.

• This tool can directly change and format your code using

  !black filename.py 

  Note that you may need to explain flake8 takes a very specific file path (in the assignment it required the code: !flake8 /home/jupyter/source/assignment7/sampling.py

• Show them the code that's been changed with black formatting

• Explain that since pep8 and black follow different style guides, if we rerun flake8, there still may be code that isn't being formatted by the black style.

[hfboyce]

Function they have seen before:

def exponent_a_list(numerical_list, exponent=2):
    """
    Creates a new list containing the square values of the input list. 

    Parameters
    ----------
    numerical_list : list
        The list from which to calculate squared values 

    Returns
    -------
    list
        A new list containing the squared value of each of the elements from the input list 

    Raises
    ------
    TypeError
        If the input argument numerical_list is not of type list

    Examples
    --------
    >>> exponent_a_list([1, 2, 3, 4])
    [1, 4, 9, 16]

    """
    if not isinstance(numerical_list, list):
        raise TypeError("You are not using a list for the numerical_list input.")

    if not all(type(element) is int for element in numerical_list):
        raise TypeError("The elements in numerical_list must all be of type int")

    new_exponent_list = list()
    for number in numerical_list:
        new_exponent_list.append(number ** exponent)
    return new_exponent_list

[hfboyce]

Tests they have seen before

assert exponent_a_list([1, 2, 4, 7], 2) == [1, 4, 16, 49], "incorrect output for exponent = 2"
assert exponent_a_list([1, 2, 3], 3) == [1, 8, 27], "incorrect output for exponent = 3"
assert exponent_a_list([], 3) == [], "incorrect output for empty list"
assert exponent_a_list([1, 12, 3], 0) == [1, 1, 1], "incorrect output for exponent 0"
assert exponent_a_list([1, 2], -2) == [1, 0.25], "incorrect output for a negative exponent"

Tests in separate functions

def exponent_2_test():
    assert exponent_a_list([1, 2, 4, 7], 2) == [1, 4, 16, 49], "incorrect output for exponent = 2"

def exponent_3_test(): 
    assert exponent_a_list([1, 2, 3], 3) == [1, 8, 27], "incorrect output for exponent = 3"

def empty_list_test():
    assert exponent_a_list([], 3) == [], "incorrect output for empty list"

def exponent_0_test():
    assert exponent_a_list([1, 12, 3], 0) == [1, 1, 1], "incorrect output for exponent 0"

def exponent_neg_test():
    assert exponent_a_list([1, 2], -2) == [1, 0.25], "incorrect output for a negative exponent"

[hfboyce]

Function that doesn't pass tests

def bad_function(numerical_list, exponent=2):
    new_exponent_list = [numerical_list[0] ** exponent] # seed list with first element
    for number in numerical_list[1:]:
        new_exponent_list.append(number ** exponent)
    return new_exponent_list

Tests

assert bad_function([1, 2, 4, 7], 2) == [1, 4, 16, 49], "incorrect output for exponent = 2"
assert bad_function([2, 1, 3], 3) == [8, 1, 27], "incorrect output for exponent = 3"
assert bad_function([], 2) == [], "empty list"

[hfboyce]

Bad Code

x = {  'a':37,'b':42,
'c':927}
very_long_variable_name = {'field': 1,
                        'is_debug': True}
this=True

if very_long_variable_name is not None and very_long_variable_name["field"] > 0 or very_long_variable_name['is_debug']:
 z = 'hello '+'world'
else:
 world = 'world'
 a = 'hello {}'.format(world)
 f = rf'hello {world}'
if (this): y = 'hello ''world'#FIXME: https://github.com/python/black/issues/26
class Foo  (     object  ):
  def f    (self   ):
    return       37*-2
  def g(self, x,y=42):
      return y
# fmt: off
custom_formatting = [
    0,  1,  2,
    3,  4,  5
]
# fmt: on
regular_formatting = [
    0,  1,  2,
    3,  4,  5
]